Elektrische und strukturelle Charakterisierung von einzelnen Kern-Mantel Halbleiter Nanodrähten
Zusammenfassung der Projektergebnisse
The aim of this project was to test the impact of an atomic force microscopy (AFM) probe, performing electrical measurements, on the structural properties of single coreshell nanowires (NWs) by measuring X-ray diffraction (XRD) patterns before and after studying the NWs by AFM under different applied forces and currents. It was motivated by the fact that the pervious electrical measurements by using focused ion beam (FIB) apparatus (see paper) resulted in local changes of the crystal structure and the generation of defects. For this purpose, Be-doped GaAs NWs have been grown by molecular beam epitaxy (MBE) at Paul Drude Institute in Berlin and GaAsSb/GaSb and GaSb-InAs NWs have been grown at Lund University by metalorganic chemical vapor deposition (MOCVD) technique. Structural investigation of NWs has been performed mainly at PETRA III (DESY) using a nanofocus X-ray beam in the order of 100nm (1μm?!) and highly brilliant synchrotron radiation which did allow for phase retrieval to retrieve the spatial strain distribution within a single NW. Electrical characterizations have been done at Lund university using A Bruker Dimension Icon AFM in conductive AFM mode for imaging the nanowires and measuring current-voltage curves at specific positions on top of the NW. By performing structural measurements before and after the electric probe at same NWs the impact of AFM tip and electrical current on the NW was studied. As result of this project we could demonstrate at InGaAs/GaAs NWs that in most cases electrical measurements by AFM did not generate defects. The structure of NWs before and after the electrical measurements were the same. For GaAsSb/GaSb and InAs/GaSb NWs we measured the spatial distribution of electrical current cross the basal plane in order to identify local variations of axial current close to the core-shell interface. Unfortunately, additional structural investigations were not possible at this system because respective beamtime proposals were not successful. In addition, the proposed experiment bringing an in-situ AFM to a synchrotron beamline in order to perform in-situ electrical measurements combined during the XRD nanoprobe were not successful because of various technical problems which could not be overcome. These problems can be summarized by, first, missing overlap between AFM tip and X-ray beam, and second, generation of charge carriers by the x-ray beam. Because the project time did coincide with the CORONA pandemic many experiments were delayed (restricted access) or even not possible (no beamtime). Fortunately, PETRA III offered compensation of beamtime at later time. In order to fit to these experimental phases, the project duration was stretched several times. Unfortunately, the data are currently not evaluated completely.
